Contrary to popular belief, the robot's special effects are completely practical (it is actually a working remote-controlled prop) and do not have any CGI at all.
BB-8's design is based in an early original concept by Ralph McQuarrie for the design of R2-D2 during the production of the first Star Wars film from the 70s. Since that design's effects were too complex to create at the time, another more simple was used instead.
